Marking instrument



FIG. 1 is a left side elevational view of a marking instrument showing my new design, the right side being a mirror image thereof;

FIG. 2 is a rear elevational view;

FIG. 3 is a front elevational view;

FIG. 4 is a bottom plan view;

FIG. 5 is a top plan view; and,

FIG. 6 is a top plan view of a second embodiment of my new design, all other views being identical to FIGS. 1 through 4. 

The ornamental design for a marking instrument, as shown and described. 